Louvers having various structures have been provided in the art. Without exception, the louvers of the art have been designed to be mounted in a single manner, with the vanes thereof being disposed in an outward and downward inclined disposition in a prespecified direction in order that the louver will properly shed precipitation and protect against the weather. No louver structure has been provided in the art which is adaptable for mounting in reversed dispositions, with the louver in each disposition being capable of sheding precipitation and protecting against the weather. The louvers of the art are of fixed dimensions, whereby for each louver size a separately designed louver must be provided. Examples of louver structures known in the art are shown in U.S. Pat. Nos. 2,862,439, 3,021,778, 3,248,837, 3,302,554, 3,580,160, 3,584,566, 3,645,195, 3,866,375, and 4,103,601, none of which shows a louver disposable for use in reversed directions, and none of which shows a louver structure formed by modular elements whereby its size may be varied. This invention seeks to provide a louver disposable in reversible dispositions, and constructed such that it may be of diverse sizes.